Presentation on theme: "Chapter 9 S,S&L T&S Section 3.5 Terry Ring University of Utah"— Presentation transcript:
1 Chapter 9 S,S&L T&S Section 3.5 Terry Ring University of Utah Heat IntegrationChapter 9 S,S<&S Section 3.5Terry RingUniversity of Utah
2 Lost Work = Lost Money Transfer Heat from T1 to T2 ΔT approach Temp. for Heat ExchangerTo= Temperature of EnvironmentUse 1st and 2nd laws of ThermodynamicsLW=QToΔT/(T1T2)ΔT=T1-T2To= Environment TemperatureQ= UAΔTlm=UA (ΔT1-ΔT2)/ln(ΔT1/ΔT2)T1QT2
3 Simple Heat Exchange Network (HEN) Use another stream for HX instead of a utility.What happens when delta T in Exchanger is lowered? To Zero?
4 Costs Heat Exchanger Purchase Cost Annual Cost CP=K(Area)0.6 CA=im[ΣCp,i+ ΣCP,A,j]+sFs+(cw)Fcwim=return on investmentFs= Annual Flow of Steam,$5.5/ston to $12.1/ston = sFcw=Annual Flow of Cold Water$0.013/ston = cwCpA is HX in auxiliary networks
5 Capital and Operating Cost Optimization Capital cost goes down when A is less. This is caused by delta T being larger for Q to remain the same.
6 Heat Integration Make list of HX Instead of using utilities can you use another stream to heat/cool any streams?How much of this can you do without causing operational problems?Can you use air to cool?Air is a low cost coolant.Less utilities = smaller cost of operations
25 Too Many Heat Exchangers Sometimes fewer Heat exchangers and increased utilities leads to a lower annual costNHx,min= Ns + NU - NNWs=No. streamsU=No. discrete UtilitiesNW=No. independent Networks (1 above the pinch, 1 below the pinch)Solution to Too Many Heat ExchangersBreak Heat Exchanger LoopsStream SplittingAttack small Heat Exchangers First
26 Stream Splitting Two streams created from one 1Two streams created from oneone heat exchanger on each split of stream with couplings11b1a1b1a
41 Heat Pumps How do they work? Carnot Efficiencyηmax= 1-Tc/ThEndoreversibleη =1-√(Tc/Th)Same as Air ConditionerConvert low temperature heat to high temperature heat.Must add work as heat can not go up hill.
42 Heat Pumps/Heat Engines Heurisitcs When positioning heat engines, to reduce the cold utilities, place them entirely above or below the pinchWhen positioning heat pumps, to reduce the total utilities, place them across the pinch.
43 Heat Pumps Where can they be used? HeuristicWhen positioning heat pumps, to reduce the total utilities, place them across the pinch.
44 Heat Engines Where can they be used? TpHeuristicWhen positioning heat engines, to reduce the cold utilities, place them entirely above or below the pinch